Electric signal pulse controlling circuits



1941- .A. D. BLUMLEIN ET AL 2,258,732

ELECTRIC SIGNAL PULSE CONTROLLING CIRCUITS Filed Dec. 22, 1938 INVENTURS AD- BLUMLE/N EL. C. WHITE ATTORNEY Patented Oct. 14, 1941 r 2,258,732

UNITED STATES PATENT OFFICE ELECTRIC SIGNAL PULSE CONTROLLING CIRCUITS Alan Dower Blumlein, Ealing, London, and Eric Lawrence Casling White, Hillingdon, England, assignors to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application December 22, 1938, Serial No. 247,164 In Great Britain December 24, 1937 2 Claims. (01. 178-73) This invention relates to electric signal pulse device places substantially no load on the concontrolling circuits and is concerned with imtrolling circuits.

movements in or modifications of the invention The invention may be employed to provide a described in co-pending application Serial No. unidirectional conducting switch or a switch 194,542 filed March 8, 1938 in the name of W. S. 5 which is bi-directionally conductive. In the lat- Percival and E. L. C. White. ter case two sets of three valves may be em- In the said application there is disclosed a ployed, the cathodes of one of said sets being conswitch which may be employed. for a variety of nected together, whilst the anodes of the other purposes. This arrangement comprises a pair set are similarly connected together, the two sets of uni-directional conducting devices which unbeing connected back-to-back. Controlling der the operation of controlling impulses act as pulses are applied to the cathode of one valve of an uni-directional switch. One of the electrodes one set and similar controlling pulses reversed of one of said uni-directional devices is connected in phase are applied to the anode of one valve to a like electrode of the second uni-directional of the other set. conducting device, the common electrodes being In a modification of this bi-directional conconnected to a conductive impedance. Switching ducting switch, instead of applying the controlpulses are applied to one or more of the elecling pulses through the two diodes, these diodes trodes of said arrangement so that the switch is are omitted and the controlling pulses are applied rendered conductive or insulating. through suitable impedances.

The object of the present invention is to pro- In order that the said invention may be clearly vide an improved switch of this type which reunderstood and readily carried into effect it will quires controlling pulses of smaller amplitude now be more fully described with reference to than those of the co-pending arrangement and the drawing wherein:

which operates in a quicker and improved Figure 1 shows one form of the present infashion. vention, and

The switch described in the co-pending applii ures 2 and 3 Show modifications of the circation is a uni-directional conducting device and cu t s o in Figure a further object of the present invention is to Figure 1 shows an arrangeme Using three provide an improved bi-directional conducting thermionic diode rectifiers 23, 24 and 25 (which switch. may be a triple-diode valve) the cathodes of According to the present invention an electrical Which are joined to a resistance 21 connected switching circuit adapted to be controlled by to a source of negative potential (not shown). switching pulses is provided comprising three Any other form of rectifier may be used, but if uni-directional conducting devices having effechigh speeds of switching are required rectifiers tively a common electrode which is connected to of low capacity are desirable. The three diodes an impedance, the arrangement being such that form a switch adapted to effectively connect the when a controlling pulse is applied to one of said line 2! with the line 22 (the potentials of the two devices, one or both of the other devices is or lines are made identical) under the control of are switched from a substantially non-conductcontrolling pulses applied to terminal 32 and ing condition to a conducting condition, or vice thus efiectively at point 26. The anode of diode versa 23 is connected to the line 2! and the anode of In one form of the invention the three cath valve 25 is connected to line 22. The terminal odes of three diode valves may be connected 32 is associated with the control grid of valve gether and the controlling pulse may be applied 28 to It is coupled by a fuitableacoFd-enser to an anode of one of the diodes, if desired, from J and gr leak The.cathode Valve $3 is taken a further valve. Alternatively, three diode valves :3, g gfg ig giiggs f iz g g gfg gg ig g; 3 :2, igz g iiz gi gg gg gzg g g fig g figg 2? potential via resistance 29. The resistance 29 is one of the diodes. In another form of the invenr0 27 tion triode or other multi-electrode valves may be used With the cathodes connected tOgQthe-T- This from diode cathodes to a negative potential. If last arrangemen s e advantage that as the the potential of point 25 is made more positive controllin pot nti are p d t t control than the potentials of 2| and 22 then all the curelectrode, or electrodes, of the valve or valves, the rent in impedance 21 flows through diode 24.

2 1 Should point now be driven negatively the current in the impedance 21 tends to make diodes 23 and 25 conduct since the cathodes of these diodes are driven in a negative direction, thus providing conducting paths between lines 2| and 22 and the common cathodes. If 2| and 22 are greatly different in potential the current in the impedance 21 will only flow through one or the other of diodes 25 or 25, but this current will tend to draw the lines 2| and 22 together in potential.

In a particular application it may be necessary to charge, or alter the potential on, a condenser (shown connected between line 22 and earth) to a potential which is representative of the potential of the line 2| during certain periods of time when the device is made operative. The ungrounded plate of condenser 3i) is connected to a source of positive potential by a high resistance 3|. In this case the anode of diode 24 is normally maintained positive with respect to its cathode by means of the resistance 22. The current from impedance 21 then flows through diode 24 and the diodes 23 and 25 are non-conducting, since the anode of diode 24 and consequently the cathode of 24 makes the cathodes of diodes 23 and 25 positive with respect to their anodes. The valve 28 is arranged to drive the anode pc int 2% in a negative direction when a positive controlling pulse is applied to the grid of valve 28. When point 25 is driven negatively the anode of diode 24 and therefore its cathode are also driven negatively. The cathode potential of diode 24 falls negatively until diode 23 or 25 conducts and robs diode Suppose, for instance, that during the operative period the potential of line 2| is less than the potential of line 22. The diode 25 will conduct and decrease the potential of condenser 30 negatively until the anode of diode 25 drops in potential to the same potential as the anode of diode 23. This latter diode will then conduct and if 2| is connected to a low impedance potential source (the potential of which may be varying), the change in the potential of condenser 3|] will cease and lines 2| and 22 will have been effectively joined, i. e. they are both brought to the same potential. If the potential of line 22 is negative with respect to line 2| however, and if line 2| is connected to a low impedance source of potential so that the current through impedance 21 cannot bring the potential of line 2| to that of line 22. the two lines will not be effectively joined. A leak resistance 3| from a source of positive potential is therefore connected to line 22 in order to make the potential of condenser 30 more positive, so that each time the device is operative a more negative charge is applied to condenser 3|], so that the potential of line 22 follows that of line 2| during the operative period.

The diodes of Fig. 1 may, if desired, be connected in a reverse sense so as to charge 30 positively instead of negatively. With all three diodes reversed, i. e., with the cathodes separate and the anodes connected together, the impedance 21 must be taken to a source of positive potential and resistance 3| to a source of negative potential. The valve 28 will then require a negative pulse to be applied to its grid in order to switch the device into the operative condition.

The arrangement illustrated in Fig. 2 is a modification of the circuit of Fig. 1. In this figure the diodes 23 and 24 are replaced by triode valves the grid of valve 23 being connected to line 2| and the grid of valve 24 being taken to point 26. The

24 of the current flowing in impedance 21.

anodes of the two triodes are taken to suitable sources of positive potentials. The end of the common impedance 21 is taken to a suitable negative potential. The impedance of 21 should preferably be larger than the reciprocal of the mutual conductance of the valves 23 and 24 and thus the cathode potentials of the valves 23 and 24 tend to follow the potentials applied to their grids. For this reason the valves 23 and 24 will be termed cathode follower rectifiers. The action of this circuit is similar to the three diode arrangement of Fig. 1 except that no load need be thrown on line 2| or on point 26. The condenser 30 will not be charged or have applied thereto a potential exactly equal to that of line 2| as there will be a difference of potential representing the grid bias on valve 23 necessary to pass the current through impedance 21. An advantage of this arrangement is that the pulses applied at 26 need not be very large in amplitude and they need not be as large as the signals on line 2|. For example, if point 26 is driven in a positive direction in order to keep the device inoperative, and a large signal on line 2| drives the grid of valve 23 very positive, then 23 will conduct and the current flowing through valve 24 will be reduced. This will not aiiect the condenser 33 since the cathode of valve 25 will be made positive with respect to its anode. If line 2| makes a large negative excursion, it will have no effect on the potential of the cathode of valve 23 or of valve 25. If, however, point 26 is driven negatively so that valve 24 insulates for any working potential of condenser 36, the current in impedance 21 will alter the charge on condenser 3|] in a negative direction through diode 25 until the cathode of valve 25 and therefore the cathode of valve 23 falls so low in potential that valve 23 passes all the current through impedance 21. Similar remarks apply to the arrangement of Fig. 1 except that large positive potentials on line 2| will make valve 23 conduct thus loading line 2|. Of course, if 2| is fed from a low impedance source this is immaterial. If, however, it is required not to load line 2| when the switch is inoperative, a sufliciently positive potential must be applied to the cathode of valve 23 to prevent it from conducting for any positive potential excursion of line 2 I.

The arrangement of Fig. 2 may be adapted to be use for observing devices as required in British Patent No. 458,585 and as switched conductors as in British Patent No. 449,242. In the latter case, the diode 25 is connected to the condenser in the signal lead and the grids of valves 23 and 24 to a fixed potential and to the pulse source.

The arrangement of Figure 2 can be modified by replacing either valve 23 or valve 24 by a diode valve, in which case a valve of the so-called double-diode-triode type may be employed for the three unidirectional conducting devices.

Fig. 3 shows two devices such as are shown in Fig. 1 connected back to back to form a two-way (bi-directionally conductive) switch. When operative, diodes 23, 25, 23 and 25' serve to efiectively join lines 2| and 22 for current flow in both directions. Negative and positive potentials are applied to impedances 21 and 21 respectively and to maintain the device inoperative (that is, to open-circuit the switch) positive and negative controlling potentials are applied to terminals 26 and 26' respectively. If termi nals 26 and 26 are made respectively negative and positive of the potentials of line 21 and 22, the currents in impedances 21 and 21' are diverted into the diodes 23, 25 and 23, 25' in such a direction as to draw the potentials of 2! and 22 together. If the rectifiers dilTer slightly in the potentials at which they begin conducting there may be a possible potential difference between 2| and 22 where, say, 23 and 23' are conducting and 25 and 25 are insulating due to these difierences in the rectifiers. This difficulty can be overcome by inserting small resistances directly in series with the rectifiers 23, 25, 23', and 25. Such resistances increase the resistance of the switch between 2| and 22 but prevent any such efiect as that described. It will be appreciated that push-pull pulses are required at terminals 26 and 2d and such pulses may be obtained from such a push-pull amplifier or by any other suitable form of pushpull pulse generator.

Similarly the arrangement of Figure 2 can be adapted to form a two-Way conducting switch by connecting two such arrangements back-toback.

According to a modification of the invention the two diode valves 24 and 24' of Fig. 3 can be omitted and the controlling pulses can be applied to the ends of the impedances 2'! and 2'! in push-pull; alternatively, the pulses may be applied directly to the cathodes of the valves 23 and 25 and to the anodes of valves 23' and 25, also in reversed phase, from a high impedance push-pull source of pulses in parallel with the impedances 27 and 2?, equivalent to applying pulses pedances 2i and 27 of slightly lower values.

The device of Fig. 3 may be used for charging a condenser, for example, at 22 to the potential of line 2! during the operative period, the device being capable of charging and discharging the condenser so that no leak resistance is required.

Various other modifications may be made in the present invention without departing from the spirit and scope thereof, and it is desired that any and all such modifications be considered within the purview of the present invention except as limited by the hereinafter appended claims.

We claim:

1. An electron switch circuit comprising a pair of electron discharge devices each including a which in effect is in series with imof the cathodes together, means for connecting the anodes to a pair of conductors of dissimilar potential, means including a high impedance for maintaining one of the conductors at a positive potential with respect to a point of fixed potential, a condenser connected between the said one conductor and the point of fixed potential, a third electron discharge device ineluding a cathode and an anode, means for connecting the cathode of said third electron discharge device to the cathodes of the said pair of devices, means including an impedance for connecting all of the cathodes to a source of potential negative with respect to said point of fixed potential, means for maintaining the anode of said third discharge device positive with respect to said cathodes and with respect to said tial applied thereto, and means for intermittently impressing negative control potential impulses on the anode of said third discharge device whereby, during the application of the control impulses, the potential of the said one conductor may be intermittently brought to the potential then present on said other conductor.

2. An electron switch circuit for use in a television receiving circuit wherein pictur and synchronizing signals are received and wherein an automatic volume control voltage is developed in accordance with the intensity of the received synchronizing signals comprising a pair of electron discharge devices each including a cathode and an anode, means for connecting each of the cathodes together, means for connecting the anodes to a pair of conductors of dissimilar potential, means including a high impedance for maintaining one of the conductors at a positive potential with respect to a point of fixed potential, a condenser connected between the said one conductor and the point of fiXed potential, a third electron discharge devic including a cathode and an anode, means for connecting the cathode of said third electron discharge device to the cathodes of said pair of devices, means including an impedance for connecting all of the cathodes to a source of potential negative with respect to said point of fixed potential, means for maintaining the anode of said third discharge device positive with respect to said cathodes and with respect to said pair of conductors, the other of said pair of conductors being adapted to have the received synchronizing signals applied thereto, and means for intermittently impressing negative ductor whereby, during the application of the control impulses, the potential of the said one conductor may be intermittently brought to the potential then present to develop an automatic volume control voltage ALAN DOWER BLUMLEIN. ERIC LAWRENCE CASLING XVHITE. 

